January 01, 2006

 

 Hoping for the best, preparing for the worst - January 1, 2006

 
posted December 15, 2005
 

With the recent arrival of the "Asian bird flu" in the Balkans, public health officials across the globe are hastily laying plans for the possibility—indeed, the inevitability, to many—the lethal virus will mutate into a new strain capable of sustained, person-to-person transmission.

For now, however, human infection by H5N1 avian influenza virus is uncommon. Moreover, the virus isn't particularly adept at passing from birds to people. Nevertheless, experts warn H5N1 has all the makings of a worldwide public health crisis, and the World Health Organization is sounding the alarm that a major flu pandemic could be imminent.

This worst-case scenario is understandable in light of how more than half the 120 people who contracted H5N1 have died. Moreover, wild ducks and other migratory waterfowl are natural reservoirs of the virus and, unlike domestic poultry, very resistant to infection. Then there's the uncanny knack influenza viruses have for mutation and reassortment, allowing them to combine with other strains to create new, potentially more virulent variations.

Shared fears of a flu pandemic brought hundreds of representatives of 115 countries and nearly two dozen intergovernmental and nongovernmental organizations to WHO headquarters in Geneva, Switzerland, this past November. The WHO, Food and Agriculture Organization of the United Nations, World Organization for Animal Health (OIE), and World Bank had convened to discuss ways of reducing and preventing the spread of H5N1 in poultry as well as what to do were a flu pandemic to happen.

Also that month, the Bush administration requested $7.1 billion from Congress for research and a national stockpile of vaccines and antiviral drugs to use in the event of a worldwide outbreak.

As the primary health professionals for animals, veterinarians must be part of any plan protecting people and animals from avian influenza. Many are experts in avian medicine and pathology. Veterinarians working in the poultry industry are trained in disease identification and familiar with methods for ensuring biosecurity.

The AVMA Governmental Relations Division in Washington, D.C., brought this and other lessons home to lawmakers and their staffs by hosting avian disease expert Dr. David E. Swayne for an informational luncheon on Capitol Hill, Nov. 15.

Dr. Swayne is director of the Southeast Poultry Research Laboratory in Athens, Ga. Part of the Department of Agriculture's Agriculture Research Service, the facility is where exotic and emerging poultry diseases are studied. Along with explaining why veterinarians are a vital resource for dealing with avian influenza, Dr. Swayne sought to separate fact from fiction about the virus, reports of which have led to many misconceptions.

Birds are susceptible to 16 serotypes of influenza A virus. They are not all the same, nor are they all as lethal as H5N1, Dr. Swayne explained. The highly pathogenic H5 and H7 subtypes have caused 24 "bird plagues" around the world since 1959. They are extremely contagious and often fatal. Birds infected with one of the low-pathogenic subtypes may show no signs of illness.

The Asian bird flu is unlike other avian influenza viruses encountered in the past 50 years, Dr. Swayne said. Avian flu epizootics typically begin when wild birds carrying a low-pathogenic influenza virus pass the virus to domesticated chickens, turkeys, and ducks. Over time, the virus mutates, eventually becoming a virulent strain that domestic poultry are highly susceptible to, whereas wild birds are less so.

What makes the Asian H5N1 strain so difficult to contain is its ability to pass from infected poultry to wild birds, which spread the virus along their migratory routes. "The Asian virus is much different because this virus has readapted from domestic poultry back into wild birds," Dr. Swayne explained. "Some of the recent outbreaks that have occurred in eastern Europe and western Asia are a result of migratory birds carrying the virus between very distinct geographic regions."

The ongoing H5N1 epizootic first emerged in Hong Kong in 1996 and then spread through Southeast Asia—where the virus is now endemic—to Russia and Mongolia. Turkey, Romania, and Croatia are the most recent countries invaded by the virus. Dr. Swayne noted that the toll in avian life is estimated at around 100-200 million, a number certain to increase along with the number of countries.

Another factor contributing to the current bird flu contagion is Asia's poultry production system. In the United States, poultry production is mostly an integrated system in which some 9.3 billion birds are raised indoors annually. Yet in Asia, the largest segment of poultry production occurs within villages. "They're raised either as scavengers, roaming freely, or as many as 20 birds will be confined to a home," Dr. Swayne said.

Additionally, cock fighting is a major sport in some countries. In Vietnam and China, domestic duck and geese production are large industries—China alone produces 67 percent of the world's ducks and 90 percent of the geese. Raised outdoors, these birds are exposed to wild and potentially infectious birds, Dr. Swayne said.

"Human infections by avian influenza viruses have been very, very rare," Dr. Swayne said, noting that, between 1959 and October 2005, 241 people had contracted the virus, of which 72 cases were fatal.

In Hong Kong, Vietnam, and Thailand, the human cases of H5N1 infections were associated with small, privately owned poultry flocks and live poultry markets. People contracted the virus as a result of either exposure to seemingly healthy yet infected poultry or by direct contact with sick or dead poultry.

Dr. Swayne stressed how travel, preparing or eating poultry meat, exposure to infected persons, and working on large poultry farms have not resulted in infection.

The illegal importation of an infected bird, say an eagle or fighting cock, is one of the more worrisome possibilities of H5N1 introduction. Chances of a migratory bird, meat import, or ill person sparking an avian influenza epizootic in the United States are remote, Dr. Swayne said.

Last year, U.S. Immigration and Customs Enforcement confiscated approximately 200 birds attempted to be smuggled into the country. Fortunately, none of the birds was infected, Dr. Swayne said. Still, they are a reminder about the need for remaining ever vigilant when the conventional wisdom of the public health community is a flu pandemic is just a matter of time.